Covering for drafting rollers

ABSTRACT

A spinning machine drafting device includes a pressure roller loaded against a lower roller such that a fiber structure is conveyed between the roller pair. The pressure roller has an outer circumferential layer disposed around an inner circumferential layer of different low friction material as compared to the outer layer. The outer layer is thinner than the inner layer and disposed around the inner layer so as to slide relative to the inner layer upon rotation of the pressure roller in operation of the drafting device.

FIELD OF THE INVENTION

The invention relates to a roller drafting device for spinning machinesin which the covering for the pressure rollers consists of an outer andan inner layer and the outer layer has a thinner wall than the innerlayer, as well as to a belt or casing for use as a covering for pressurerollers in such drafting devices for spinning machines in which thethinner-walled outer layer loosely surrounds the thicker inner layer sothat the outer layer can move relatively to the inner layer.

BACKGROUND

During the drafting of fiber bands in drafting devices, the clampingaction of the roller pairs plays a decisive part for the transfer of thedrafting forces onto the fiber band. The roller pairs of the draftingdevice therefore consist of a fluted steel cylinder, the so-called lowercylinder, and of a pressure roller, the so-called upper roller, that ispressed by load onto the steel cylinder. As a rule, this pressure rollercomprises an elastic covering so that no clamping line is produced butrather a clamping surface formed by the deformation of the elasticcovering, which surface brings about a significantly better fiberretention. A good clamping action is exerted on the fiber structurewithout damaging the fibers. Experience has shown that soft rollercoverings therefore yield better drafting results since the softer thecovering is, the greater is the clamping surface. However, soft rollercoverings have the disadvantage that they wear down very rapidly andthat grooves are produced in particular in the area of the fiberpassage. This so-called “shrinking” is eliminated by buffing over theentire covering surface. This alters the geometry of the drafting devicerollers and therewith also the covering properties, which for its parthas a disadvantageous effect on the drafting conditions and thus on theyarn values. In addition, the regrinding of the roller coverings is aquite expensive measure.

The attempt has therefore already been made to counteract thisdisadvantage by means of a multi-layer roller covering. DE 1 815 739 Uteaches a pressure roller whose elastic jacket is subdivided into atleast two layers of which the outer layer is designed as an elasticcasing consisting of a thin hose that can be drawn over the elasticjacket of the pressure cylinder. The designing of the outer layer as ahose makes it easy to draw a cover over the elastic jacket and also toeasily remove it from the latter when this outer circumferential surfacehas become worn. The fixing of the elastic hose is ensured by thenatural friction between rubber and rubber. This known design does makeit possible to readily replace the elastic outer layer; however, it wasnot able to solve the problem of the rapid wear and of the shrinking.

DE 1 685 634 A1 teaches a covering for drafting device rollers ofspinning machines which covering is composed of two superposedcylindrical layers of which the outer layer is harder and has a thinnerwall than the inner layer. The two layers are adhered to one another. Asa result thereof, very different materials can be combined with eachother in order to avoid the formation of windings and electrostaticcharging. However, it turned out that the problem of a good draftingability and of wear were not satisfactorily solved. In addition, as aconsequence of the adhesion the changing of the outer layer isexpensive.

SUMMARY

The invention has the problem of eliminating these disadvantages and offinding a roller covering that has high wear resistance and long-lastingelasticity in the running layer and thus ensures optimal draftingconditions for a long time. Additional objects and advantages of theinvention will be set forth in part in the following description, or maybe obvious from the description, or may be learned through practice ofthe invention.

It surprisingly turned out that it is important in a multi-layercovering with a thin outer layer and a thicker inner layer that arelative movement can take place between the two layers. The millingmotion of the soft covering and the tension forces produced thereby arethen transferred only onto the inside of the outer, thin-walled layerbut not on the fibers and the fluted cylinder. Practically no wearoccurs any more, in particular no groove formation (shrinking), so thatthe outer layer has a service life that is more than three times longerthan certain prior devices discussed above.

The outer layer is advantageously adapted on its outside as a fibercontact surface to the requirements of a good fiber clamping and on itsinside as a running surface to the smoothest possible, low-frictionrunning of the pressure roller. This is achieved, e.g., in a simplemanner by the selection of appropriate material compositions for thefiber contact layer and the running layer of the outer layer. This outerlayer can be designed as the casing around the inner pressure rollerlayer as well as an endless belt. It must only be so flexible that itadapts to the deformation of the soft inner layer. It proved to beespecially advantageous to design the outer layer in the direction oftravel of the fiber structure, that is, transversely to the roller axis,as inelastically as possible, that is, with the lowest possibleextensibility. The tension forces in the clamping surface producing wearand acting negatively on the drafting are eliminated in this manner,whereas the outer layer can adapt in the axial direction to therugosities of the fiber structure. An excellent clamping is achieved inthis manner. The desired reduction of the expansion of the outer layertransversely to the axis of the pressure roller is achieved quite wellby a yarn insert without limiting the expandability in the direction ofthe roller axis. The relative motion between the outer layer and theinner layer is favored by the smoothest possible surface of the runninglayer of the outer layer, and as a consequence thereof the breakdown ofthe tension forces is furthered in an even better manner.

It is advantageous for a high delivery speed to use an outer layerdesigned as a belt and to run this belt through a deflection rail. Inaddition, this deflection rail can also comprise side rims for a morereliable guidance. It also proved to be especially advantageous at highdelivery speeds for a trouble-free travel if the belt rolls off thepressure roller at an angle α>30° to the plane of the fiber structure.The belt advantageously consists of several layers and the inside isdesigned as a smooth travel layer and the outside as a fiber contactlayer. A yarn insert is provided between the layers which prevents thebelt from expanding in the direction of travel without adverselyinfluencing a desired transverse expansion.

Further details of the invention are explained using the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows the design of the two-layer roller covering in longitudinalsection in accordance with the invention.

FIG. 2 shows a cross section through the device according to FIG. 1.

FIG. 3 shows the design of the outer layer as belt.

FIGS. 4, 5 schematically show the design of the outer layer with aninsert for stiffening in the direction transverse to the cylinder axis.

FIG. 6 shows in section the guidance of the belt by means of adeflection rail.

FIG. 7 shows a plan view accompanying FIG. 6

DESCRIPTION

Reference is now made in detail to embodiments of the invention, one ormore examples of which are illustrated in the drawings. Each embodimentis provided by way of explanation of the invention, and not as alimitation of the invention. For example, features illustrated ordescribed as part of one embodiment may be used with another embodimentto yield still a further embodiment.

In FIGS. 1, 2 pressure roller 3 is arranged above drafting devicecylinder 5 and comprises covering 2 permanently connected in a customarymanner to pressure roller 3. Drafting device cylinder 5 and pressureroller 3 form the exit roller pair of a drafting device running at ahigh speed in accordance with the delivery. Another coating 1 isprovided as an outer layer over this inner layer coating 2 of pressureroller 3. This outer layer consists in the embodiment shown here ofthin-walled casing 1 consisting of flexible material that behavespractically without expansion relative to the material of inner layer 2in the direction of travel of casing 1. This casing 1 is slipped looselyover inner layer 2 of pressure roller 3 so that intermediate space 6 canform in the non-loaded area between inner and outer layers. It isessential that casing 1 can move relative to inner layer 2 of pressureroller 3. On the other hand, inner layer 2 is drawn firmly onto pressureroller 3, as is customary. Under the loading of pressure roller 3 softinner layer 2 is pressed onto drafting device cylinder 5 and deformed,so that no linear contact with drafting device cylinder 5 takes placebut rather an area or planar support takes place. Since outer layer 1 isthin and flexible, it adapts to the deformation of inner layer 2 withoutbeing substantially compressed itself. Therefore, in contrast to theinner layer, no appreciable pressing work is performed in the case ofouter layer 1. The clamping surface generated by the deformation ofinner layer 2 is transmitted by outer layer 1 so that fiber structure F(FIG. 6) provided for the drafting is clamped by this clamping surfacewhen passing through roller pair 3, 5.

In the customary pressure roller coverings, a clamping surface is formedby the soft elastic covering which surface produces a good clampingaction. However, tension forces are produced in the area of the clampingsurface by the pressing work of the covering that have a negative effecton the fiber structure during drafting and also cause the known highwear of the covering. However, the arrangement of an outer layer 1 thatflexibly adapts to the deformation of soft and elastic covering 2 ofpressure roller 3, but that causes no or only a very low pressing workon account of its lower thickness and deformability, surprisingly led tothe result that this outer layer 1 exhibits a significantly greaterstability and also the soft inner layer 2 displays none of the customaryphenomena of wear and shrinking. It turned out in extensive tests thatouter layer 1 still ran without any problems even after three times therun time and did not have to be replaced. The drafting values were evenable to be improved compared to new traditional coverings. It is to beassumed that this surprising result can be traced to the fact that thetension forces conditioned by the pressing work of soft and elasticinner layer 2 of pressure roller 3 can not affect the clamped fiberstructure. These tension forces are degraded by the relative motion thatis possible between soft inner layer 2 and smooth run layer 102 (FIG. 4)of outer layer 1. No relative movement takes place between the fibersand drafting device cylinder 5 as well as outer layer 1 so that theclamping takes place in the area of static friction. Thus, no wearcaused by sliding can occur.

In the exemplary embodiment according to FIGS. 1, 2 the outer layer isdesigned as cylindrical casing 1. However it can also be designed as arather long endless belt. This cylindrical casing 1 as well as a belt 10or 100 can be readily replaced in case of wear or the formation ofgrooves in the area of fiber structure F. FIG. 3 shows endless belt 10that surrounds pressure roller 3 with its soft elastic inner layer 2 andis guided by deflection rail 4. The construction as a rather longendless belt 10 or 100 and its guidance by deflection rail 4 proved tobe particularly advantageous when the device is run at high deliveryspeeds.

It should be taken into consideration that, depending on the particulardraft, drafting devices 3, 5 forming the delivery roller pair runapproximately 20 to 30 times more rapidly than the roller pairs arrangedin front of the main drafting field, that are customarily surrounded byfiber guide belts. These known fiber guide belts proved to be unsuitablefor being used as outer layer 1 on exit roller pair 3, 5. These beltsare insufficient in their properties. Thus, it turned out, e.g., that itis important that outer layer 1 or belt 10 or 100 is as inelastic aspossible in the direction of travel of fiber structure F, that is,transversely to roller axis 31, so that it can not expand.

Of course, not every expansion can be eliminated in the physical sensebut it should be as small as possible. This achieved in a simple mannerby yarn insert 103. Furthermore, the known belts favor the sliding ofthe fibers during drafting, which is undesired for the exit roller pair.

FIG. 4 shows the design of outer layer 1, 10 or 100 in section, that isdirected specifically toward these desired properties. The outer layerdesigned as casing 1 or lengthened endless belt 10 or 100 isadvantageously composed of several layers: Of fiber contact layer 101and of run layer 102. Yarn insert 103 is arranged between both layers101, 102 for eliminating the expansion in the longitudinal direction,which insert is firmly connected to fiber contact layer 101 and also torun layer 102. Fiber contact layer 101 is designed in its surface and inits material in contact with fiber structure F for receiving theretention forces necessary during drafting. This is achieved, e.g., byusing a material like the one used for pressure roller coverings. On theother hand, run layer 102 is provided with a smooth surface favoringsliding, in order to make possible a relative motion relative to outerlayer 100, 10 or 1 around inner layer 2. A material favoring sliding ispreferably used for run layer 102 like the material used, e.g., for theknown belts for fiber guidance in the main drafting field.

Yarn insert 103 takes the elasticity from belt 100 in the direction oftravel so that an expansion is practically not possible. However, theexpandability remains transversely to the direction of travel, that is,in the direction of pressure roller axis 31. The belt can adapt to therugosities of drafted fiber structure F so that a good clamping isalways ensured. In spite of these multi-layers of the outer layer, thelatter must naturally not be too thick in order to impart goodflexibility to it for adaptation to the deformation of inner layer 2 andto fiber structure F. A total thickness of 0.8 to 1.0 mm has proven tobe especially advantageous in this connection as regards the stabilityand also the drafting results. No groove formation (shrinkage) could bedetermined even after several years of run time.

The desired properties of run layer 102 and a fiber contact layer 101can also be achieved by an appropriate physical shaping of the surfaces.However, run layer 102 and fiber contact layer 101 preferably consist ofdifferent materials that have the desired sliding properties and thenecessary grip. Measurements according to DIN 53375 have shown thate.g., the above-described material for fiber contact layer 101 has africtional force value that is at least twice as high as the frictionalforce value of run layer 102 when the latter consists of a material likethat used for belts for fiber guidance in the main drafting field. Runlayer 102 thus has good sliding properties while fiber contact layer 101achieves an excellent clamping of the fibers.

The manufacture of such an endless belt in accordance with FIGS. 4,5takes place, e.g., in such a manner that at first run layer 102 isapplied onto a tubular body with a circumference corresponding to thelength of the belt, onto which run layer a yarn is wound that forms yarninsert 103. Then, this yarn insert 103 is covered with fiber contactlayer 101.

In the embodiment according to FIGS. 6, 7 a belt 100 is run throughdeflection rail 4. In order to ensure a light run of belt 100,deflection rail 4 is not only rounded but additionally provided with alow-friction coating. Cage 42 with guide rims 41 follows this deflectionrail 4. The space between deflection rail 4 and drafting device roller 3is encapsulated by this cage 42 and its guide rims 41, so thatcollections of fluff in this space are avoided. Belt 100 runs fromdrafting device roller 3 at an angle α relative to the plane of fiberstructure F. This avoids turbulence and fly formation in the exit areaof fiber structure F. Cage 42 is supported on holding rail 44 viapressure springs 43 so that deflection rail 4 exerts a tension on belt100. Side rims 41 serve to laterally guide belt 100. An easy and rapidreplacement of belt 100 is also possible in this embodiment. Belt 100 isrelieved by pressing deflection rail 4 back and can also be readilylifted over side rims 41. These side rims 41 also serve in addition toencapsulating the space between pressure roller 3 and deflection rail 4for the lateral guiding of belt 100. If outer layer 1 of pressure roller3 is arranged asymmetrically to fiber structure F, outer layer 1 can beturned so that the left side is located on the right side and thus fiberstructure F runs over an unused surface of the outer layer.

It should be appreciated by those skilled in the art that variousmodifications and variations can be made to the embodiments of theinvention described herein without departing from the scope and spiritof the claims or their equivalents.

1. A spinning machine drafting device, comprising: a roller pair including a pressure roller loaded against a lower roller such that a fiber structure is conveyed between said roller pair for drafting; an inner layer of a deformable flexible material attached completely around the circumference of said pressure roller without relative movement between said inner layer and said pressure roller; an outer circumferential layer of a generally inelastic material disposed around at least a portion of the outer circumference of said inner layer, said outer layer being thinner than said inner layer and disposed around said inner layer so as to slide relative to said inner layer upon rotation of said pressure roller in operation of said drafting device.
 2. The drafting device as in claim 1, wherein said outer layer comprises a casing that completely surrounds said inner layer.
 3. The drafting device as in claim 1, wherein said outer layer comprises an endless belt that runs in a traveling direction around a circumferential portion of said pressure roller.
 4. The drafting device as in claim 1, wherein said outer layer comprises an inner run material disposed against said inner layer, and an outer fiber contact material that contacts a fiber structure conveyed between said roller pair.
 5. The drafting device as in claim 4, wherein said inner run material is formed of a smooth low friction material to facilitate relative sliding movement between said outer and inner layers.
 6. The drafting device as in claim 5, wherein said outer layer comprises substantially no expansion in a direction transverse to the rotational axis of said pressure roller.
 7. The drafting device as in claim 6, further comprising an insert material disposed between said inner run material and said outer fiber contacting material, said insert material formed of a material to minimize expansion of said outer layer in the direction transverse to the rotational axis of said pressure roller.
 8. The drafting device as in claim 5, wherein said outer fiber contacting material is formed of a high frictional material as compared to said inner run material to facilitate clamping of a fiber structure.
 9. The drafting device as in claim 1, wherein said outer layer comprises an endless belt that runs in a traveling direction around a circumferential portion of said pressure roller, and further comprising a deflection rail disposed to guide said endless belt in said traveling direction.
 10. The drafting device as in claim 9, wherein said deflection rail comprises a rounded surface formed of a low friction material in an area where said endless belt contacts and is deflected by said deflection rail.
 11. The drafting device as in claim 9, wherein said deflection rail is resiliently mounted so as to apply a tensioning force to said endless belt.
 12. The drafting device as in claim 9, wherein said deflection rail comprises lateral side rims for lateral guidance of said endless belt.
 13. The drafting device as in claim 12, wherein said lateral sides rims are configured to encapsulate space between said deflection rail and said pressure roller and surrounded by said endless belt.
 14. The drafting device as in claim 9, wherein said endless belt is guided at an angle away from a running plane of the fiber structure at an angle of greater than about 30 degrees with respect to the running plane of the fiber structure.
 15. The drafting device as in claim 9, wherein said endless belt comprises an outer fiber contacting material having dimensions so as to be asymmetric relative to the dimensions of the fiber structure so that an unused portion of said outer fiber contacting material is provided in use of said drafting device, wherein said endless belt is repositioned to bring said unused portion into contact with the fiber structure.
 16. An outer layer component for use in a covering combination over a pressure roller of a pair of rollers in a drafting device for spinning machines, wherein the covering combination includes an inner layer formed of a flexible and deformable material disposed entirely around the pressure roller with essentially no relative movement between the pressure roller and inner layer, and the outer layer component is disposed around at least a portion of the circumference of the inner layer and slides relative to the inner layer upon rotation of the pressure roller in operation of the drafting device, said outer layer component formed from a generally inelastic material and being thinner than the inner layer said covering comprising substantially no expansion in a direction transverse to the rotational axis of said pressure roller.
 17. The outer layer component as in claim 16, wherein said component is a casing configured to fit completely around the pressure roller.
 18. The outer layer component as in claim 16, wherein said component is an endless belt that runs in a traveling direction around a circumferential portion of the pressure roller.
 19. The outer layer component as in claim 16, comprising an inner run material disposed to lie against the inner layer of the covering combination, and an outer fiber contact material that contacts a fiber structure conveyed against the pressure roller.
 20. The outer layer component as in claim 19, wherein said inner run material is formed of a smooth low friction material to facilitate relative sliding movement between said outer and inner layers.
 21. The outer layer component as in claim 19, further comprising an insert material disposed between said inner run material and said outer fiber contacting material, said insert material formed of a material to minimize expansion of said outer layer in the direction transverse to the rotational axis of the pressure roller.
 22. The outer layer component as in claim 19, wherein said outer fiber contacting material is formed of a high frictional material as compared to said inner run material to facilitate clamping of a fiber structure.
 23. The outer layer component as in claim 22, wherein said inner run material has a frictional value of about one-half the frictional value of said outer fiber contacting material.
 24. The outer layer component as in claim 16, wherein said component is an endless belt that runs in a traveling direction around a circumferential portion of the pressure roller, said endless belt comprising an outer fiber contacting material having dimensions so as to be asymmetric relative to the dimensions of the fiber structure so that an unused portion of said outer fiber contacting material is provided in use of said drafting device, wherein said endless belt is repositioned to bring said unused portion into contact with the fiber structure.
 25. A method for manufacturing the outer layer component of claim 21, comprising applying the inner layer onto a tubular body having a circumference equal to a desired inner circumferential dimension of the endless belt, applying the insert material in the form of a yarn wrapped over the inner layer; applying the outer layer over the yarn insert material; and removing the endless belt from the tubular body. 